Why Were There Not More Widespread Auroras This Past Week?

If you’ve been looking at the news recently, you may have read about a supersized sunspot which is still just about visible on the solar surface. The sunspot, named AR2192, is so huge that it was visible to the “naked eye” during the partial solar eclipse last week. (Please remember to never look directly at the Sun!) It is estimated to be around 14 times the size of the Earth – which makes it the largest sunspot since 1990.

Now, you may have read that sunspots are good indicators for the Sun’s activity and that a high activity is a good sign for aurora. This past week, there have been aurora sightings; auroras are often visible at a high magnetic latitude- even during low solar activity. These “everyday” auroras, as we like to call them, can be quite remarkable and are visible on most clear nights. However, with this spectacular, historic sunspot, we were hoping to see an enhanced aurora that is visible at lower magnetic latitudes. So why were there no enhanced auroras this past week?

Well, it’s important to note that the sunspot has been active. In fact, this sunspot has produced multiple solar flares (some of which have been very large). Solar flares are huge bursts of energy in the form of solar radiation (e.g. X-rays, UV light). These solar flares have been causing havoc, creating strong radio blackouts around the globe affecting communications and GPS satellites; however, there have been no significant auroral displays.

That’s because for aurora to occur, we also need a burst of energetic particles to be released from the Sun, known as a coronal mass ejection (CME). Although the link between flares and CMEs is not altogether understood, CMEs often accompany flares. Somewhat surprisingly, though, for this sunspot we have seen multiple flares but no CMEs.

Scientists studying the magnetic field on the Sun may have figured out why. Although this sunspot region is huge, it is not particularly complex. In fact, as far as sunspots go, this one is pretty simple to understand – a textbook example you might say!

The photo on the right is from NASA’s Solar & Heliospheric Observatory spacecraft and shows the polarity of the Sun’s magnetic field (taken on October 24, 2014).

That big blob, split half black and half white, near the center of the Sun is the sunspot (also circled in yellow). The black and white colors indicate opposite magnetic polarities (i.e. North/South). Since the black and white regions are very well defined (and not jumbled up together) it shows that the magnetic field is almost dipolar (i.e. it has two poles) and that the magnetic field is not twisted, distorted or complex. Our understanding is that for CMEs to be released we need a twisted, distorted field – so, in this case, a CME is unlikely.

Does that mean that this sunspot won’t produce significant auroras in the future? Well, no.

Sunspots evolve and change over time; the magnetic field configuration may become more twisted and might result in a CME release. However, it’s important to note that as the Sun rotates, the sunspot will start to face away from the Earth (at least for another fortnight or so) and so any CMEs would not be Earthward directed.

It just goes to show that we can never be sure, ahead of time, when a beautiful aurora will occur.

If you’d like to learn more about sunspot complexity or help scientists understand their complexity, check out the following citizen science project: http://www.sunspotter.org/

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Nathan is a space weather scientist based at NASA’s Goddard Space Flight Center. As a core member of the Aurorasaurus team, he is primarily responsible for merging traditional forms of space weather data with citizen science observations to improve the nowcasting ability of the auroral oval models – though you may also see the occasional blog post or Facebook update from him too!